The present invention relates to catalytic compositions for esterification, transesterification and polycondensation reactions, a process for the catalysis of said reactions employing such catalytic compositions and polyesters or resins obtainable by this process.
Catalytic systems containing organotin compounds are widely known.
E.g. compounds of the formula [(RSn)12O14(OH)6]2+ are described mainly in connection with their interesting structure in: H. Puff, H. Reuter, J. Organomet. Chem. 1989, 373, 173-184; D. Dakternieks, H. Zhu, E. R. T. Tiekink, R. Colton, J. Organomet. Chem. 1994, 476, 33-40; S. Durand, K. Sakamoto, T. Fukuyama, A. Orita, J. Otera, A. Duthie, D. Dakternieks, M. Schulte, K. Jurkschat, Organometallics 2000, 19, 3220-3223.
Compounds of said type [(RSn)12O14(OH)6]2+ are further described to show a poor performance in catalyzing or activating reagents and compounds within the acetylation reaction of acetic anhydride with an alcohol (S. Durand, K. Sakamoto, T. Fukuyama, A. Orita, J. Otera, A. Duthie, D. Dakternieks, M. Schulte, K. Jurkschat, Organometallics 2000, 19, 3220-3223.)
It is known for compounds of the formula [(BuSn)12O14(OH)6]2+ when stored in methanol, that a replacement of two structural important μ2-bridged OH groups of the cluster against OCH3 units can occur (D. Dakternieks, H. Zhu, E. R. T. Tiekink, R. Colton, J. Organomet. Chem. 1994, 476, 33-40).
Furthermore is known that during the production of polyesters for some applications for example wrappings and technical yarns, a crystallization and polycondensation in the solid state is carried out (U.S. Pat. No. 4,064,112, U.S. Pat. No. 4,263,425, U.S. Pat. No. 5,362,844). In other applications, fibers or filaments are spun directly and direct preforms are produced in a process wherein an intermediate transfer into the solid state and a repeated remelting is not applied.
Conventional polyester compositions are connected with a series of disadvantages (general summary in: Handbook of polyester thermoplastics, 1st edition, Wiley-VCH, Weinheim, 2002). Among these disadvantages are in particular:    Necessity of high temperatures for the synthesis    High catalyst concentration (100-500 ppm [as metal])    Degradation processes under processing and polycondensation conditions; for example formation of vinyl esters and due to the formation of acetic aldehyde in polyethylene terephthalate (PET), formation of acrolein in polypropylene terephthalate (PPT) and tetrahydrofuran formation in polybutylene terephthalate (PBT).    Limited use of the catalyst systems, dependent on the technology of the process and the chemical structure of the substrate; classic titanium based catalysts cannot be added for example during the esterification- and/or pre/condensation step, as these are readily hydrolyzed to inactivate titanium oxides.    Application of the catalyst system only in selected process stages for example only during the esterifications- or only during the transesterification- or only during the polycondensation stage.    Optical turbidity of the produced polyester for example by deposits of elementary metal impurities as this can occur by the use of antimony based catalyst systems.    Discoloration of the polyester by the catalyst itself, for example titanium based catalyst systems cause a yellow coloring of the polymer or formation of chromophor by-products, respectively.    Problematic metering and addition of catalysts and catalyst formulations.